Co-planar loud speaker



Oct. 21, 1958 HARRls 2,857,478

(IO-PLANAR LOUD SPEAKER Filed Sept. 13, 1954 2 Sheets-Sheet 1 mvem-roulJACK s. "Aw

ATTOIQNGI Oct. 21, 1958 J. B. HARRIS co-PLmAR LOUD SPEAKER 2Sheets-Sheet 2' Filed Sept. 13, 1954 I NV enl'ro a, JACK 5. HA

United States Paton-t 2,857,478 CO-PLANAR LOUD SPEAKER Jack B. Harris,Toronto, Ontario, Canada, assignor to Radio Speakers (Canada) Limited,Toronto, Ontario, Canada, a corporation of Ontario Application September13, 1954, Serial No. 455,651 4'Claims. (Cl. 179-116 frequency range manyworkers have disclosedarrange' ments employing concentric piston arrays,two or more air impelling agencies being usually tied to the same motoror voice coil. This has not'proved satisfactory to discriminatinglisteners for the reason that, although by this means cone break-up isdiminished, there remains a substantial degree of amplitudeintermodulation distortion to which trained human ears are quitesensitive. This form of distortion is'due to the fact that while thevoice coil is moved out of the dense part of the fixed magnetic fieldunder'the urge of a low-frequency wave of high intensity, the voice coilis also urged to oscillate, while so disposed, at a high frequency,and'at a considerably lower intensity. Normally such oscillations occurcontinuously while the voice coil is moving in and out of the field atthe lower frequency. The result is that the higher frequencies aremodulated in amplitude by the low frequency impulse, causing a spuriousharmony which the human ear readily detects'as an objectionable quantitynot scored in the music; engineers have already taken great pains toprevent such intermodulations from existing in the wave translationnetworks of the sound systems and it has been rather discouraging to'find these distortions turning up in the speaker system itself.

Efforts have been made, in another direction, to provide severalindependent speakers, separately disposed spacially and to connect thedriving coils in different parts of a frequency separating network sothat each of a plurality of speakers receives only a restricted'range'of'friequencies suited to its particularly select'edtalent's'. This hasproved to be a better arrangement'but has displayed a new fault almostequally noxious to the'ear: this fault may be described asinstrument-creep. When" listening to systems of this type on, fore'xamplebrchestial music, when the dynamicrange of the music is great,the instruments seem to be moving about in the listening' room in a mostdisconcerting manner as the sound volume of the various instrumentsvaries. This has been found due to the habit of arranging so-calledtwo-Way and 3- way speaker systems with a considerable spacial '1disposition of the respective units. Whereas some workers; notablyBriggs and Klipsch have provided multi-way arrangements in which thiseffect has been reduced, the price at which this hasbeen'achievedhas-'provedfiosbe very high.

It is an object'of this invention to providea'low'cost multi-wayreproducer system wherein a plurality' of? 27,851,478 Fatented Oct. 21,1953 speakers, each operating independently overa specified range offrequencies, are grouped spacially in over-lapping relation so that thevarious frequencies are initiated from a restricted area. This providesthe well known, hole in the wall effect so widely heldas a desirablecontribution to realism in the presentation of recorded sound in smallrooms, and avoids both the phenomenon of instrument-creep, and alsoentirely eliminates amplitude'intermodulation products from the speaker"system when supplied with distortion-free electric wave energy.

It is another object of the invention to provide a S tem of the kindproposed wherein the various speaker units are so disposed one with theother that the whole ensemble can be treated as though'it we're a singlespeaker of current size and form, thereby making the present arrangementcapable of being substituted in aiieiiis n g single-speaker equipmentWithout any modification thereto other than an exchange of the old unitfor the new one.

The variousingenious means whereby these objects are achieved will bemore readily understood by perusal of" the following description of atypical construction in accordance with my invention, the text beingaided by reference to the accompanying'drawings wherein:

Figure l is a perspective View of a complete two-Way speaker system inaccordance Withmy invention.

Figure 2 is a side elevation'p'artly in section of'a speaker systemaccording to my invention.

Figure 3 is a face view looking into the spacially overlapping conesofmy arrangement.

Figure 4 is a side elevation of a pair of tweeter'un'its" forming partof the arrangement depicted inthe previous figuresand showing'especiallythe stepped support bracket" whereby the tweeters are nested withintli'e arch or the woofer cone.

Figure 5 is a perspective plan view of mounting brackets and tweeterchassis arranged in accordance with my invention.

Figure 6 depicts in detail a preferred method of liriiig'-' ing thesignal leads through the woofer cone and onto the terminals of thetweeter units.

Referring now to these figures, 1 is'a' in'ai-n woofer frame ofconventional form having mounting holes '21, 22, 23, 24 which conformto' the manufacturing standards currently approved by the American-Radio and Television Manufacturing Association. The woofenassenibly maybe of the size marketedat this time as a'twe'lv'e inch unit; the driverpiston and motor may have a combined mass and characteristic such as toprovidea' resonant tendency in the region of 50 cycles, and'a-usefuPresponse, when fitted to a suitable bafiie or enclosure, offrom 30cycles to 5000 cycles; this is a pr'eferred but not limitingspecification.

The tweeter units are, typically, of the kind' welt ers reside centrallywithin the arch" of thew'oofr frame" lthe holes 21, 23 therein coincidewith the holesZl',

23 and the support members are eyeletedto the'woorer frame so thatclearance holes in the eyelets onowtne holes 21, 23 to be used formounting'the'wliole 'assernbly in a cabinet in the same manneras'iS'c0m""mOI11Y pi'a tised in'connection with conventional singlespeaker units; In order tonirther this latter object, the brackets" 4; 5

are stepped inwardly at 10' so" that the tweeters do "n'dtfl extendbeyond the plane of the woofer frame; i e., be

yond the gasket face 'oftlie WOOfCf;

In a-further aspect the tweeter frames 8*, 9*are di'sposed within thearch of the woofer so thattheir respective planes intersect to bound anexterior angle of approximately 200 degrees so that the cones 2, 3radiate a dispersed train ofsound waves. f

The motors and pistons of the tweeters are, in a typical case arrangedtohave a" useful frequencylrange from about 3,500 cycles to 17,000 cyclesin a preferred but not limiting specification. A capacitor 19 isconnected in series with a feed wire to the tweeters which nominally areconnected in parallel and are phased so that their respective cones movealways in the samedirection under the urge of a wave of energy. Thecapacitor 19 functions to restrict the influence of frequencies below thdesired operating range of the tweeters, in the manner well known. Thethree speakers are all normally connected in parallel to the loadconnections 16, 17, with the modification that capacitor 19 is insertedin series with the tweeters as and for the purpose above noted. Thecombined phasing is normally such as to cause all the speaker cones 2, 3and 20 to move co-phasally, when connected by 7 lines 28, 29 to theaudio signal wave source designated 30.

A feature .of the invention resides in the manner in which the feederwires to the tweeters have been conducted through the woofer cone 20 tothe terminal board 25. It is desirable to keep these leads short, veryflexible, and so nearly free from resonant eifects as possible. Thelatter requirement is one which has plagued workers in this field formany years. In large speakers, and, in fact, in any speaker wherein thevoice coil leads are required to be of any substantial length there is atendency for them to whip and cause buzzy sounds which can be heard bythe listener. These buzzy noises occur at certain frequencies only andare excited by the rhythmic excursions of the cone, particularly at thehigher frequencies. In normal constructions designed to cover a widefrequency range one end of each voice coil lead is necessarilystationary at the load terminal, and the other end moves with the cone.

In the present construction, by passing the voice coil leads to the highfrequency speakers through the woofer near its apex'and sealing them tothe cone 20 with cement, as at 20', where they pass through, the leadsto the tweeter are made shorter than they would otherwise be and theytherefore are less liable to buzz since the changes in attitude thereofare never influenced by th tweeter frequencies directly, since theirmoving ends cillate only at the lower fi'equencies of the woofer cone20. The tweeters being small, their own leads to their respectiveterminal boards 26, 27 are short and, these speakers being of provendesign, the buzz problems have already yielded tov manufacturingexperience. Thus the newconcept has not introduced any new problems oflead buzz, I e I The respective voice coil impedances of the threemotors can be arranged in such a manner that the relative sound outputsare in good balance.

This may be accomplished by suitable choice of voice coil impedances,suspensions and the magnetic flux densities in the air gaps. Thesetechniques are well known,

per se, to those skilled in the art.

It will be evident that the arrangement is not limited to two-wayoperation. One or other of the tweeter frames, 8, 9 may contain adifferent cone and voice coil system such that the one tweeter mayfunction as what is currently referred to as a middler, or middlefrequency range reproducer. This unit may also include low frequencyand/ or higher frequency attenuators so as to provide three electricaldivisions thereby providing three independent acoustical 'channels-athree-way system. If the middler is designed to operate usefully only inthe range above 500 cycles, experience has shown that no baifie, per se,is necessary so the present construction is readily adaptable to such amodification,

It will also be evident that the tweeters may be bridged across theadjustable arm of a potentiometer whose max- The construction abovedescribed may be made up to employ smaller or larger speakers and, asimplied herei inbefore, the smaller speakers having ranges of operationlimited to regions above 200 cycles, and for the purposes of thisspecification defined as tweeters may be of respectively differentsizes. In another aspect thelargerp speaker which for the purpose ofthis specification I de-.

fine as a woofer may have its upper frequency range extended to includeat least a portion of the band con-' stituting the lower region of thefrequency range assigned to the said tweeters; this and similararrangements. canbe varied without departing from the spirit of myinven-i tion as defined in the appended claims- What is claimed is:

1. A loud speaker arrangement comprising a conical woofer characterisedby a chassis including a mounting ring, a pair of tweeter units eachcharacterised by a mounting frame and positioned to reside side by sidewithin the arch of the woofer cone and laterally within the boundariesof said ring, a pair of V-shaped brackets having;

" their respective apices attached to selected points on the peripheryof said mounting ring and having their respective outer arms bentinwardly toward the woofer cone and then turned transversally thereof,means attaching respective ends of said arms to corresponding points onthe mounting frames of said tweeters, means for joining the tweeter.frames rigidly at adjacent sides of said tweeterv frames, the mountingbrackets and attaching means being so disposed as toposition the saidtweeters centrallywithin the said woofer mounting ring so that the facesof said tweeter mounting rings lie in planes which intersect to includea selected angle, and circuit and terminal means for connecting therespective voice coils of the Woofer and tweeters jointly to an electricwave source.

2. A loud speaker arrangement in accordance with claim 1 the mountingbrackets and attachment means cooperate to position said tweeterscentrally within said of substantially 160 degrees.

3. A construction in accordance with claim 1 in which the respectivewoofer andtweeter voice coils are con- 1 5:, nected in parallel to saidcircuit means, and in which the.

relative disposition of said woofer and tweeter voice coils enables allthe cones to vibrate to-phasally at any frequency to which they areall'responsive.

4. A construction in accordance with claim 1 wherein 0 there is providedin said circuit means a frequency selecq tive facility located betweenthe woofer voice coil and at least one of the tweeter voice coils tolimit the response I of such tweeter voice coil to a specified range offre-.,

quencies.

0 References Cited in the file of this patent UNITED STATES PATENTS2,053,364 Engholm Sept. 8, 1936 7 2,453,521 Marquis Nov. 9, 1948 OTHERREFERENCES Audio Engineering, October 1949, vol. 33, pg. 55..

Audio Engineering, October 1950, page 23.

Audio, Coaxial Speaker Assembly, March'1954, vol. 38, pgs. 48, 50. i

This is useful as it facilitates a sometimes desirai; woofer mountingring with the faces of said tweeter-1 mounting rings disposed inintersecting planes at an angle 1

